[PATCH] selinux: fix NULL pointer dereference in selinux_sctp_bind_connect()

[Tristan Madani <tristmd@gmail.com>]

From: Tristan Madani <tristan@talencesecurity.com>

selinux_sctp_bind_connect() reads sk->sk_socket and passes it to
selinux_socket_bind() or selinux_socket_connect_helper() without
checking for NULL.  When an SCTP ASCONF chunk is processed in softirq
context on a socket that has been concurrently closed, sock_orphan()
will have already set sk->sk_socket to NULL.  The subsequent
dereference of sock->sk at offset 0x18 triggers a kernel panic.

Add a NULL check on sk->sk_socket before use.

Fixes: d452930fd3b9 ("selinux: Add SCTP support")
Cc: stable@vger.kernel.org
Signed-off-by: Tristan Madani <tristan@talencesecurity.com>
---
 security/selinux/hooks.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index 0f704380a8c8..e45588563caa 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -5717,6 +5717,9 @@ static int selinux_sctp_bind_connect(struct sock *sk, int optname,
 
 	/* Process one or more addresses that may be IPv4 or IPv6 */
 	sock = sk->sk_socket;
+	if (!sock)
+		return -ECONNRESET;
+
 	addr_buf = address;
 
 	while (walk_size < addrlen) {
-- 
2.47.3